1.Field of the Invention
The present invention relates to a video signal recording medium playing apparatus for playing a recording medium such as a video disk or the like on which a video signal has been recorded.
2.Description of the Related Art
In recent years, a video disk playing apparatus which commonly uses an image memory so as to execute two functions has been developed as an apparatus for playing a recording medium on which a video signal (what is called a composite video signal) is recorded. The above apparatus will now be described with reference to FIG. 1. In FIG. 1, while a video disk 2 is rotated by disk rotating means including a spindle motor 1, a carrier signal having a video signal (which assumes an NTSC signal here) recorded on the video disk 2 is obtained by a pickup 3 which is positioned in the radial direction of the disk 2. A demodulator 4 obtains the original video signal by demodulating the carrier signal. An A/D converter 5 converts the original video signal into the digital signal and supplies to a time base correcting circuit 6. A memory controller 7 executes a time base correction by writing and reading out the digital signal in cooperation with a system controller 8 synchronously with a reference vertical sync signal and a reference horizontal sync signal (hereinafter, abbreviated to REFV and REFH, respectively) which are generated from a signal generator 9. The digital video signal which was transmitted through the memory controller 7 is supplied to one fixed contact A of a switch 11 of a noise reducing circuit 10.
The system controller 8 controls the operation in the normal reproducing mode (hereinafter, referred to as a noise reducing mode or the special reproducing mode to search, scan, or the like in accordance with a mode designation command from a manual operation section 23 such as a keyboard or the like.
Now, assuming that the noise reducing mode has been set, a movable contact of the switch 11 is connected to the fixed contact A side as shown in the diagram by a command from the system controller 8. Therefore, the digital video signal is supplied to input terminals of subtracters 12 and 13 through the switch 11. An output of the subtracter 12 is supplied to a Y/C separator 14, by which the digital video signal is separated into a luminance component and a chrominance component. The luminance component signal is supplied to a D/A converter 15 and is output as an analog luminance signal and is supplied to a display driving section (not shown). The chroma component signal is supplied to a chroma inverter 17 and a D/A converter 16 and is output as an analog chrominance signal and is supplied to the display driving section. The chroma inverter 17 inverts the phase of the chrominance component every on a 2-field unit basis, that is, every other frame on the basis of field information from the memory controller 7. The chrominance component which is issued from the chroma inverter 17 is supplied to one input terminal of an adder 18. The luminance component from the Y/C separator 14 is supplied to the other input terminal of the adder 18 and is again synthesized with the chrominance component is supplied to a switch 19.
A movable contact of the switch 19 is connected to a fixed contact B side by the system controller 8 in the noise reducing mode. Therefore, an output of the adder 18 is transmitted through the switch 19, and is written into a field memory (hereinafter, simply referred to as a memory) 21 while excluding the playback V sync (simply referred to as PBV hereinafter) because of cooperation between the memory controller 7 and an NR controller 20, so as to save the memory capacity of the memory 21.
On the contrary, when reading out of the memory 21, a reference V sync (simply referred to as REFV hereinafater), is inserted in place of the PBV. In the noise reducing mode, the PBV is given as a reset signal from the time base correcting circuit 6 to the signal generator 9, so that the phases of the REFV and PBV are coincident with each other.
The one-field preceding video signal which has been read out from the memory 21 is supplied to the subtracter 13 and a subtraction is executed between the one-field preceding video signal and the video signal which is supplied from the memory controller 7. Although the phase of the chrominance component in the NTSC video signal is inverted every frame, the phase of the chrominance component has been inverted every other frame as mentioned above. Therefore, the phases of the chrominance components in the one-field preceding video signal and the video signal of the present field which are used for the subtraction coincide with each other.
A difference signal resulted from the subtraction is supplied to a non-linear circuit 22. In the noise reducing mode, an operation command is supplied from the NR memory controller 20 to the non-linear circuit 22 and the noises are reduced in accordance with the level of the difference. On the other hand, when the difference level is equal to or higher than a predetermined level, the difference is considered to be caused by a motion in a video image bt not the noise components, so that the noise reducing operation is stopped. Such a process is performed by using a fact that as the noises in the displayed video image are visually conspicuous as the motion in the video image is small, that is, the level of the video signal difference of a field unit is small. Therefore, the noise reducing operation can be executed without sacrificing the motion information in the video image. Such a noise reducing operation has already been well known by Japanese Patent Publication No.62-3639. Therefore, its detailed description is omitted.
An output of the non-linear circuit 22 is supplied to the subtracter 12 and the noise-reduced video signal is emitted from the subtracter 12 and is supplied to the Y/C separator 14.
Now, assuming that the operating mode has been set to the special reproducing mode accompanied with a jumping operation such as fast forward operation, search operation, or the like, the movable contact of the switch 11 is connected to the fixed contact B side and the movable contact of the switch 19 is connected to the fixed contact A side. Therefore, the digital video signal which was transmitted through the memory controller 7 is sequentially written into the memory 21 through the switch 19. When, in this case, video data are written into the memory 21, the memory controller 7 sets the head of the data to the head address in a predetermined storage area in the memory 21. When, a jumping operation is executed during playing of a CLV disk in which the phases of the V and H sync signals are not coincident with each other in the radial direction, the video data are sequentially read out from the head addresses and the REFV and REFH are inserted, thereby to produce a video signal representing images without disturbances.
The memory controller 7 checks continuity of subcarrier of the video signal which is read out of the memory 21 and executes a proper correction if necessary and supplies the signal to the B contact of the switch 11. In the special reproducing mode, an operation stop command is generated from the NR controller 20 to the non-linear circuit 22 and the noise reducing operation is not executed. Therefore, the digital video signal which is transmitted through the switch 11 is supplied to the Y/C separator 14 without being influenced by any signal in the subtracter 12.
When, in the above prior art, the operating mode is shifted from the noise reducing mode to the special reproducing mode, the memory 21 executes the sync converting operation and the V sync signal of the video signal which is read out is REFV. Therefore, any disturbances in the image does not occur even if the image is displayed. When, however shifting from the special reproducing mode to the noise reducing mode, the subtracter 13 compares the present video signai synchronized with the RBV and the one-field preceding video signal which is the output of the memory 21 and is synchronized with the REFV, thereby obtaining the difference between them. When, therefore there is a remarkable phase deviation between the PBV and the REFV as in the case of playing a CLV disk, the displayed reproduction image fluctuates largely.